From literature a number of routes are known for the synthesis of .alpha.-amino acid amides and the corresponding .alpha.-amino acids, in which the .beta.-position is substituted with at least one (hetero)aromatic group. The best known route, which can be-used for different .alpha.-amino acids, is the Strecker synthesis route (Introduction to Organic Chemistry, Streitwieser and Heathcock, Macmillan Publishing Co., Inc. New York, 1981). In that method a suitable aldehyde is treated with ammonia and HCN, so that an .alpha.-amino nitrile is formed, which is subsequently subjected to a hydrolysis reaction.
The aldehyde used in the preparation of phenylalanine is phenylacetaldehyde. This raw material, however, is expensive. The Strecker synthesis is therefore economically unattractive for the production of phenylalanine on an industrial scale. That is why in the past efforts were made to find alternative and economically more profitable processes for the production of phenylalanine on an industrial scale. One of these processes is based on the intermediate hydantoin. This intermediate is condensed with benzaldehyde to form benzylidene hydantoin. After hydrogenation of the double bond and hydrolysis of the hydantoin ring phenylalanine is obtained.
Although the hydantoin process is often more advantageous economically than the Strecker process, hydantoin, too, is a relatively expensive raw material and consequently less attractive economically for the preparation of phenylalanine.